A high power output is required in a transmitter such as a radar transmitter which uses solid-state elements. In the transmitter, a plurality of power amplifying devices is used. The transmitter outputs the high power by combining outputs of these power amplifiers. The radar power amplifying device is generally highly efficient. The radar power amplifying device outputs the high power by operating the solid-state elements in a non-linear region. However, when a power amplifying device is operated in a non-linear region, the output includes a fundamental wave component and, in addition, a spurious and a harmonic component. Hence, a transmitter has a filter which filters the harmonic component to suppress that the harmonic component is emitted from an antenna.
Further, the power amplifying device has a level detection detector which monitors the output (transmission power). Furthermore, the power amplifying device has an RF monitor terminal which monitors a transmission output level and an occurrence situation of a harmonic.
A conventional transmitter has one filter element at a stage subsequent of a combiner which combines outputs of a plurality of power amplifying devices. Hence, high power handling capability is required in the filter element. However, the filter element having high power handling capability is large and expensive. Hence, there is a problem that the transmitter becomes large and expensive.
When a small filter element is provided in each of the power amplifying devices, the filter element having high power handling capability does not need to be provided, and a cheap filter element can be used as the small filter. Generally, a filter element is formed by covering by a package a filter body such as a filter pattern and coaxial cables each of which connects the filter body and a connector which is an external connection terminal. When such a filter element is provided in each of the power amplifying devices, mounting space of the filter element increases, and therefore the dimension of the power amplifying device increases. Therefore, even when the small filter element is provided in each of the power amplifying devices, it is difficult to at least miniaturize the transmitter.
Further, a conventional power amplifying device has directional couplers on a line through which a high frequency signal is transmitted, and supplies one of outputs of the directional couplers to a level detection detector and a RF monitor terminal through the distributor. Hence, a harmonic produced by the level detection detector is also outputted to the RF monitor terminal. Therefore, there is a problem that it is not possible to accurately monitor a spurious of the power amplifying device.